Characterizing and identifying materials

Abstract

In characterizing or identifying an article which is provided with luminescent material, excitation radiation is directed at the article to cause emission from the luminescent material and the intensity of emitted radiation at different wavelengths is compared by directing the emitted radiation to photodetectors through a plurality of optical systems having respective filters of different wavelength transmission and comparing the modified signal level from one photodetector with the signal level from another photodetector.

I claim: 
     
       1. Apparatus for characterising an article which is provided with luminescent material, which apparatus comprises a source of excitation radiation for directing radiation at the luminescent material when the article is at a test station, a plurality of optical systems arranged to receive simultaneously radiation emitted by the luminescent material and direct the radiation to respective photodetectors, a plurality of optical filters each arranged with a different wavelength transmission and each being located in a respective one of the optical systems and arranged to pass radiation to the associated photodetector, and electrical circuit means arranged so as: (1) to receive electrical output signals derived from said photodetectors said signals varying linearly in level in accordance with the intensity of radiation incident thereon;   (2) to effect comparison of signals derived from the respective photodetectors in order to characterise the article;   (3) to provide at least one pair of signal levels defining a desired range for use in determining whether the comparison falls within a desired range, and   (4) to provide an output signal indicating the result of the comparison.   
     
     
       2. Apparatus for characterising an article which is provided with luminescent material, which apparatus comprises a source of excitation radiation for directing radiation at the luminescent material when the article is at a test station, a plurality of optical systems arranged to receive simultaneously radiation emitted by the luminescent material and direct the radiation to respective photodetectors, a plurality of optical filters each arranged with a different wavelength transmission and each being located in a respective one of the optical systems and arranged to pass radiation to the associated photodetector, and electrical circuit means arranged so as: (1) to receive electrical output signals derived from said photodetectors said signals varying linearly in level in accordance with the intensity of radiation incident thereon;   (2) to modify the signal level from one photodetector to provide at least one pair of different modified signals serving to define a required range;   (3) to compare a signal level derived from each other photodetector with a pair of modified signal levels, and   (4) to indicate when the signal level derived from each other detector is within the required range.   
     
     
       3. Apparatus for characterising an article which is provided with luminescent material, which apparatus comprises a source of excitation radiation for directing radiation at the luminescent material when the article is at a test station, a plurality of optical systems arranged to receive simultaneously radiation emitted by the luminescent material and direct the radiation to respective photodetectors, a plurality of optical filters each arranged with a different wavelength transmission and each being located in a respective one of the optical systems and arranged to pass radiation to the associated photodetector, and electrical circuit means arranged so as (1) to receive electrical output signals derived from said photodetectors, said signals varying linearly in level in accordance with the intensity of radiation incident thereon; (2) to modify the signal level from one photodetector to provide two different modified signal levels serving to define a required range; (3) to compare a signal level derived from another photodetector with each of the modified signal levels and (4) to indicate when said signal level derived from said other photodetector is within said required range. 
     
     
       4. Apparatus according to claim 3, wherein the optical systems each comprise a plurality of optical fibres. 
     
     
       5. Apparatus according to claim 4, wherein said optical systems each comprise a bundle of optical fibres, each bundle having one end arranged to direct light to a respective photodetector and the other ends of the fibres forming one or more groups, the or each group having fibres lying closely adjacent each other in a common plane and distributed so that fibres of all bundles have an even distribution at the end arranged to receive radiation from the article under test. 
     
     
       6. Apparatus according to claim 5, wherein at least one light pipe is provided for receiving radiation emitted by the luminescent material and directing the radiation to one end of the bundles of fibres. 
     
     
       7. Apparatus according to claim 6, wherein the fibres of all said bundles are connected at one end to one or more light pipes common to all the bundles, the fibres of the different bundles having an even distribution at the interface with the or each light pipe. 
     
     
       8. Apparatus according to claim 5 wherein the source of excitation radiation comprises a radiation source located adjacent at least the end of the fibre bundles arranged to receive radiation emitted by the luminescent material. 
     
     
       9. Apparatus according to claim 5 wherein the bundles of fibres are connected to two light pipes spaced apart and incident to each other so as to detect radiation from the same part of an article under test, the source of excitation radiation being arranged to direct radiation onto the article along a path symmetrically disposed between the two light pipes. 
     
     
       10. Apparatus according to claim 3, wherein the source of excitation radiation is an ultra violet source. 
     
     
       11. Apparatus according to claim 10, wherein the source of excitation radiation comprises a flash lamp. 
     
     
       12. Apparatus according to claim 11 wherein conveyor means is provided for moving a succession of articles past a test station and the apparatus includes detector means for detecting the arrival of an article at the test station and synchronising means is provided to synchronise the operation of the flash lamp with the arrival of the article at the test station. 
     
     
       13. Apparatus for characterising an article which is provided with luminescent material, which apparatus comprises a source of excitation radiation for directing radiation at the luminescent material when the article is at a test station, three optical systems arranged to receive simultaneously radiation emitted by the luminescent material and direct the radiation to respective photodetectors, three optical filters each arranged with a different wavelength transmission and each being located in a respective one of the optical systems and arranged to pass radiation to the associated photodetector, and electrical circuit means arranged so as: (1) to receive electrical output signals derived from said photodetectors said signals varying linearly in level in accordance with the intensity of radiation incident thereon;   (2) to modify the signal level from a first photodetector to provide two pairs of different modified signal levels to define first and second required ranges;   (3) to compare a signal level derived from the second photodetector with the first required range;   (4) to compare a signal level derived from the third photodetector with the second required range; and   (5) to generate an acceptance signal when the signal levels derived from the second and third photodetectors are within said first and second required ranges, respectively.   
     
     
       14. A method of characterising an article which is provided with luminescent material, which method comprises directing excitation radiation at the luminescent material on an article under test so as to cause the luminescent material to emit luminescent radiation, detecting the emitted radiation at different wavelengths by simultaneously directing said radiation through a plurality of optical systems to respective photodetectors, each optical system incorporating filter means having a selected wavelength transmission to its associated photodetector, the selected wavelengths transmission differing from that of another optical system, and each photodetector giving rise to an output signal which varies linearly in level in accordance with the intensity of the emitted radiation incident thereof, modifying the signal level from one photodetector to provide at least one pair of different modified signals serving to define a required range, comparing a signal level derived from each other photodetector with a pair of modified signal levels, and determining when the signal level derived from each other detector is within the required range.